Transcript THE CIRCULATORY SYSTEM DEFINITION/DESCRIPTION This is

THE CIRCULATORY SYSTEM
DEFINITION/DESCRIPTION
1. This is the composite body system that is
responsible for the continuous movement of
all body fluids and their contents.
1. It is subdivided into:
 Blood vascular (Cardiovascular) system and
 Lymphatic vascular system.
The Cardiovascular System
Functions: The functions of the CVS include:
1.Continuous movement of body fluids
2.Oxygen transport to body tissues
3.CO2 transport from body tissues
4.Transport of metabolic wastes
5.Transport of hormones
6.Transport of drugs and other biologically active
substances
7. Transport of blood cells
8. Thermoregulation
9. Electrolyte regulation
10. Body defense
11. Biosynthesis of biologically active substances
12. Inactivation of biologically active substances
Component Parts of the CVS
The CVS is composed of a circuit of a hollow
muscular organ (The heart) and vascular channels
through which blood flows to and from the body
tissues.
It is composed of:
1.The heart
2.The arterial vascular system
3.The capillary vascular system
4.The venous vascular system
Microscopic Anatomy of the CVS
All the component parts of the CVS share a common basic
microstructure which is found in their walls.
The wall is composed of three main layers, viz.
1. Tunica intima (Tunica internus): This is the mucous
membrane which lines the cavities of the heart and
the lumen of the vessels.
2. Tunica media (Tunica intermedus): This is composed
of striated and smooth muscle fibres which
contract to propel blood through the heart and
blood vessels.
3. Tunica adventitia (Tunica externus): This is the
fibrous connective tissue layer which supports and
protects the heart and vessels.
•Variations occur in the 3 layers from one
part of the body to another on the basis of
functional requirements of various tissues of
the body.
•The most variable layer is the tunica media.
Microscopic Anatomy of the Heart
The cardiac wall is composed of:
1.Tunica intima (Endocardium): This is lined by squamous cell
and contains blood vessels, nerve fibres and conducting
tissue in its connective tissue
2. Tunica Media (Myocardium): This is composed
of several layers of cardiac muscle fibres (Striated muscle).
3. Tunica Adventitia (Epicardium): This is lined by
serous squamous cells and contains blood
vessels, nerve fibres and adipocytes in its
connective tissue
Furthermore, the heart is enclosed in a coat of fibrous tissue
which is lined by serous squamous cells (Fibrous and Serous
Pericardium)
The Arterial Vascular System
Functions:
a. Blood distribution to tissue capillaries
b. Control of Pressure and rate of blood flow to
the tissues.
Organization:
There are three types of arteries;
1.Elastic arteries: These include the aorta and its
main branches
2. Muscular arteries: These include the named
arteries supplying regions and organs of the body
3. Arterioles: These are vessels found in the walls
and substances of organs of the body
The Microcirculation
The microcirculation consists of a network of vessels at
which:
1.Exchange of substances occurs between the blood
vascular system and the tissues of the body
2.Blood flow into tissues is controlled.
The microcirculation is composed of:
Metarterioles.
Precapillary sphincters.
Capillaries
Post-capillary venule
Collecting venule
Small muscular venule
Arteriovenous shunts
The Capillary (Exchange Vessels)Vascular system
The capillary is an endothelial-lined vessel which
also has a basement membrane.
Functions:
a. Permits selective passage of molecules.
b.Serves as the exchange site between blood
and tissues of the body.
c. It metabolizes substrates through the
endothelial cells.
d. Serves as an Antithrombogenic channel for
blood
Classification of capillaries:
There are four types of capillaries viz.
1.Continuous (Somatic) capillaries
(Pharynx,
Brain and Muscles)
2. Fenestrated capillaries with diaphragm
(Stomach and Endocrine glands)
3. Fenestrated capillaries without diaphragm
(Kidney glomeruli)
4.Discontinuous capillaries (Liver, Spleen
and Bone marrow )
The Venous Vascular System (Capacitance Vessels)
Functions:
1.Collection of blood from the capillary system
2.Return of blood to the heart for recirculation
Characteristic features of Veins:
a. Low pressure blood flow.
b. Valve assisted blood flow.
c. Skeletal muscle assisted blood flow.
d. Inspiration assisted blood flow.
e. Larger capacity than the arterial vascular
system hence retains 70 of total blood volume.
Classification of Veins:
1. Muscular venule. Smallest vein
(connecting venous system to the
microcirculation)
2. Small veins
3. Medium-sized veins and
4. Large-sized Veins
The Lymphatic Vascular System
The vessels of the lymphatic vascular system are
blind-ended tubes arising from tissue spaces.
The functions of the lymphatic system are:
1. Drainage of excess tissue fluid (Lymph)
2. Passive transport of lymph, lymphocytes and
other immunologic factors
3. Release of lymph into the blood vascular
system
Characteristic features of the lymphatic system:
This system is characterized by:
• Unidirectional flow of fluid towards the heart
• Valves and muscle assisted flow of fluid
• Filtration of fluid through lymph nodes
• Vessels formed from blind-ended lymph
capillaries
Microstructure of the Lymphatic System:
This comprises:
1.Blind-ended, thin-walled, endothelial-lined
capillaries
2. Non-fenestrated endothelium
3. Rudimentary basement membrane
4. Large vessels posses circular and longitudinal
layers of smooth muscles
5. Fine elastic filaments (Anchoring fibres) attach
endothelium to surrounding connective tissue
6. The large vessels contain vasa vasorum and
nerve fibres
Lymphatic vessels are not found in the following
areas/structures:
1. Central nervous system (CNS)
2. Cornea
3. Teeth
4. Bone
5. Cartilage
6. Bone Marrow
7. Thymus gland
8. Placenta.